The EPA is expected to propose hard targets for state-by-state reduction of carbon emissions from power plants

When the Obama administration unveils its much-anticipated proposal to curb power plant emissions, this cornerstone of the president's climate change policy — the most significant environmental regulation of his term — will not be declared in a sun-bathed Rose Garden news conference or from behind the lectern in a major speech.

It will not be announced by the president at all, but instead by his head of the Environmental Protection Agency, while President Obama adds his comments in on an off-camera conference call with health advocates.

The low-key rollout from the man who once boldly predicted his election would be remembered as the moment when "our planet began to heal" and likened the climate change challenge to the U.S. space program shows just how far the president has shifted his strategy.

After charging into office in 2009 with a goal of passing comprehensive legislation and making massive investments in alternative energy, Obama saw his reform bill tank and the government's investments in the Solyndra solar company turn into a political embarrassment. Since then, Obama and his team have retooled and climbed back slowly — too slowly, some say — with Plan B: incremental, politically cautious and legally aggressive environmental regulation, culminating in the EPA rule expected to be announced Monday.

"I think we scaled back the legislative ambition, but continued to push where we could," said Dan Utech, the White House energy and climate change advisor. "It's been an adaptive process — a process of figuring how best to push at each point in time."

Though it may be unveiled with the fanfare of a routine public health announcement, the proposed rule will mark the most significant step on climate change of Obama's presidency. It is expected to set hard targets for state-by-state reduction of carbon emissions from power plants, the single largest source of carbon pollution in the U.S.

Experts note the rule will probably spur the growth of state-level cap-and-trade marketplaces, the system Obama tried to institute on a national level in his failed legislation. In that sense it may be remembered as a rare moment when Obama worked around opposition in Congress to implement one of his top goals.

[Obama] has made this issue a centerpiece of this term. I've heard a real commitment and passion on the issue.— Frances Beinecke, president of the Natural Resources Defense Council

Obama's policies and his strategy have detractors on the left and right. Industry groups and many Republicans say the president's drive to regulate will only increase the cost of energy, kill jobs and weaken a still-fragile economy. They accuse him of stretching the current law. "They have to push the Clean Air Act much further than it's ever been used before," said Jeffrey Holmstead, an assistant EPA administrator during the George W. Bush administration.

Others complain Obama's environmental concerns do not seem to extend to the potential hazards from extracting natural gas, or the increased use of fossil fuels that could result from construction of the Keystone XL oil pipeline, a project Obama has delayed but not killed.

To be sure, evaluating Obama's legacy on the issue is premature. The rule proposed Monday will be debated over the next year. Its success in cutting carbon emission will depend on the details, how strict the targets are and how the federal government holds states to them.

U.S. emissions have been declining recently because of increased use of natural gas to generate electricity, but the country is still second to China in annual emissions. It is far from clear whether the rule will win back U.S. credibility and leverage in negotiations over an international agreement, as the White House hopes.

Current and former aides say the shift from one term to the next was driven by Obama himself. They describe the president as capable of diving deep into the science of the matter and dismissive of doubters. He often seems taken by the possibilities of renewable technology, likes to cast the development of wind and solar as potential economic drivers and frequently asks wonky questions at briefings.

"One of the last questions I remember him asking me was in a meeting with scientists and we're talking about natural gas," said Heather Zichal, who until November was Obama's top advisor on climate change. "He turns and asks, 'By the way, do we have an accurate accounting of the life cycle of [greenhouse gas] and do we need to worry about methane emissions?' It's not unusual for him to ask weedy, technical questions."

Still, the president and the White House have kept an eye on the politics of an issue that remains low on the priority list for most voters. He's careful to talk about the rising costs of extreme weather events and natural disasters, rather than ice caps and polar bears, as a way of driving the issue home. The White House is loath to use loaded labels like "environmentalist."

On Saturday, in his weekly address, Obama focused on the health risks of climate change. He said the new rules would "cut down on carbon pollution, smog and soot that threaten the health of the most vulnerable Americans, including children and the elderly."

Immediately after his reelection, the president declared his intention to make climate change a priority, aides say. He included the issue in his second inaugural speech amid some debate among his advisors about whether it would trigger economic anxiety for average Americans.

That debate roiled in the White House throughout much of Obama's first term. Obama helped Democrats in the House successfully pass a cap-and-trade bill to create a market-based system to drive down emissions, but the effort stalled in the Senate while the White House juggled its other major priority — passing an overhaul of healthcare.

Some former officials say the administration quickly turned to a regulatory approach, but how fast is a subject of debate. While the economy tanked, pushing any measure that might be viewed as a job-killer was a risk the White House wanted to avoid as the reelection campaign drew closer.

While the White House moved ahead with plans to increase fuel efficiency standards for cars and light trucks, ozone regulation was put on hold and a rule regulating coal ash stalled.

"I would say there was a period of early activity, and then, as with many regulatory matters in the administration, there was a period when that all went dark," said Lisa Heinzerling, a former top climate policy advisor at the EPA who left the administration in 2010.

Among those delayed plans was regulation of greenhouse gases from power plants. The EPA announced in 2010 that it intended to regulate coal-fired power plants as well as oil refineries. Under the timeline set, the agency would have issued final rules for both by November 2012. The deadline came and went.

The White House and advocates believe this moment is right. The natural gas boom has helped drive the transition away from coal, and the economy has improved. EPA Administrator Gina McCarthy has been working closely with utilities and other stakeholders. The public appears to back the rules.

Two-thirds of Americans support increased regulation on power plants, even if the cost of electricity rises, according to a poll conducted in April by the Yale Project on Climate Change Communication.

And Obama and his party may have learned more lessons on how to manage and package their plans. Obama will frame the issue as a matter of public health, clean air and a government agency doing its work. He'll conduct interviews on Monday with the American Lung Assn. and other health groups.

Few dispute the recent momentum behind the issue. "He has made this issue a centerpiece of this term," said Frances Beinecke, president of the Natural Resources Defense Council. "I've heard a real commitment and passion on the issue. He's putting his eggs in this basket. Now his challenge is delivering it."